This invention relates to a novel process for preparing oxaprostaglandin intermediates.
The oxaprostaglandins prepared by the process of this invention are known compounds of very high pharmacological effectiveness. For example, 16-aryloxy-prostaglandin F.sub.2.alpha. is commercially available as a highly active luteolytic for animals under the tradename "Equimate".
The synthesis of such oxaprostagladins is described in DOS's [German Unexamined Laid-Open Applications] Nos. 2,223,365, 2,322,673 and 2,606,051. These references disclose methods wherein suitable phenoxypropyl phosphonate solutions are first reacted at temperatures of -78.degree. C. with a butyllithium solution and/or with a NaH suspension under ice cooling conditions. This produces in situ a reactant of the basic formula ##STR5## Subsequently, the appropriate aldehyde ##STR6## is introduced into this mixture. R.sub.1 is H, alkyl, OH or functionally modified OH. After the latter has been worked up, the desired ketone of basic formula ##STR7## is obtained in yields of 10-40%. Even when the reaction is most carefully controlled, it is impossible to obtain reproducible yields since the reaction is carried out in situ. Thus, undesirable and uncontrollable secondary reactions occur, such as, for example, the splitting-off of the blocking group R.sub.1 when a minor excess of alkali is present.